Thermal control switch



Jan. 5, 1943. H. w. BIRK THERMAL CONTROL SWITCH Filed Oct. 51, 1940 f ij Patented Jan. 5, 1943 UNITED STATES PATENT OFFICE THERMAL CONTROLSWITCH Harold w. mu, East Hartford, em, assignor to The KartManufacturing Company, Hartford, Conn., a corporation of ConnecticutApplication October 31, 1940, Serial No. 363,660

Claims. (Cl. 200- 142) The present invention relates generally totemperature control devices and more specifically to an improvedelectric circuit breaker, including one or more normally closed electricswitches and an automatically operable breaker member for opening theswitches when the temperature of a thermo-responsive element reaches apredetermined allowable maximum. When utilizing automatic circuitbreakers of this type, it is customary to locate the thermo-responsiveelement within or adjacent to a heated chamber, as, for example, a hotwater tank, so that the temperature of the element is alwayssubstantially that of the liquid within the chamber. In order to limitthe temperature of the liquid to the allowable maximum, the switches ofthe circuit breaker are included in the electric circuit which energizesor otherwisecontrols the unit supplying heat to the chamber.

It is an object of the present invention to provide a circuit breakerfor this purpose, having a thermo-responsive element including a fusiblemetal locking member which normally secures the automatic breaker memberin an inoperative position against the action of a tensioned spring.When the temperature of the thermo-responsive element reaches theallowable maximum, the metal locking member quickly fuses, whereupon thebreaker is actuated by the tensioned spring and operates to open theswitches.

It is a further object of the invention to provide a circuit breaker ofthe type indicated, wherein'the action of the spring upon the breakermember in its inoperative position doe not impose a sumcient load todeform or produce partial failure of the fusible locking member beforethe predetermined allowable maximum temperature is reached. 4

A still further object of the invention is to provide a circuit breakerhaving the features and advantages indicated, which can be easily andinexpensively manufactured and assembled, and which can be resetfollowing actuation thereof without the replacement of any part such asthe fusible metal lock. Other objects will be input obvious and in partpointed out more in detail hereinafter.

The invention accordingly consists in the feeswitch made in accordancewith the present invention;

Figure 2 isa profile view of the switch shown in Figure 1, andillustrates clearly one way in which a switch may be operativelyattached to a device, the temperature of which 'is to be controlled;

Figure 3 is a view similar to Figure 1 with the front wall of the casingcut away;

Figure 4 is a cross-sectional view of the switch taken along line 4-4 ofFigure l and shows the switch mounted on a slightly different fittingfrom the one shown in Figure 2;

Figure 5 is a rear view of the switch with the back cover removed;

Figure 6 is a perspective view of the manually operable member of theswitch and the coopcrating positioning member therefor; and

Figure l is a perspective view of the temperature responsive elements ofthe switch partially broken away to show the parts thereof Referring tothe embodiment of the invention illustrated in the drawing, there isprovided a box-like casing C having side walls I2 and a front wall i4which are integrally formed of a moldable plastic or similar non-currentconducting material. A back cover It is secured to the free edges of theside walls I2 and provided an enclosure within which there is operablysupported a pair of electric switches l0 and a spring actuated contactbreaker B for opening the switches. A thermo-responsive element,indicated generally by the letter D, is supported in a centrallydisposed opening 20 in the back cover It and normally restrains thebreaker B in an inoperative position. I

More specifically, the front wall l4 of the casing C is provided at thefour corners with suitable recesses 28 within which are securedterminals 30 and 32 for the electric switches ll. Each of the terminals30 and 32 includes a terminal screw 33 by means of which the switches l0may be connected into the electric wiring cirbreaker. In the embodimentshown in the drawing, the switch terminals 30 are located at diagonallyopposite corners of the casing C, and support suitable resilient switcharms 34 which extend in opposite directions toward the terminals 32. Aninwardly extending contact button is secured to the free end of each arm34 and normally resiliently engages a similar button 38 carried by eachterminal 32. The front wall [4 is Figure 1 is a plan view of oneembodiment of a further provided with a centrally disposed circular hole39 in which the forward end of the contact breaker B is rotatablyjournalled. As illustrated in Figure 5, the contact breaker B- is asubstantially cylindrical member, provided along diametrically oppositeelements with a pair or outwardly extending camLning lugs 48 for forcingthe switch arms 34 away from the center of the casing C and therebybreak the engagement of the contacts 36 and 38. In assembled position,the forward ends 4| of the lugs 48 bear against the rear surface of thefront wall l4 so that the forward portion of the breaker B protrudesfrom and is journalled in the casing C.

To journal the other end of the breaker, there is provided a shaft 42having its forward end received in a centrally disposed internal breakerbearing 44 and extending rearwardly therefrom through the centralopening 28 in the back wall I6.

The breaker B is further provided with a rearwardly disposed arm 46which extends radially outward from the breaker at a 45 degree angle tothe adjacent lug 48 and is engageable with a pair of stops 48 and 58integrally formed with the casing C. As illustrated in Figure 5, thestops 48 and 58 limit the rotation of the breaker between the breakerposition X, illustrated by solid lines, and the position Y, illustratedby broken lines. When the breaker is located in the closed switchposition X, the lugs 48 are positioned midway between the switch arms34, whereas when the breaker is in the position Y each of the lugs 48cams one of the switch arms 34 outwardly so as to disengage the contacts36 and 38. As previously indicated, the switch contacts are normallyclosed and to retain the breaker in the closed switch position X, it isoperatively secured to the shaft 42 and the shaft, in turn, is normallyheld against rotation relative to the casing C by the thermo-responsiveelement D. To provide a satisfactory connection between the breaker andthe shaft, a recess 66 is formed in the rear end of the breaker and theinner surface thereof (as indicated in Figure 6) is provided with aseries of four radially disposed steps 68 located at 90 degrees to oneanother.

Positioned within the recess 56 and secured to the shaft 42. as by anon-rotatable bearing 68, is a central metal plate 66 having a pair ofresiliently upset steps 68 which cooperate with the complementary steps58 of the breaker to provide a uni-directional drive therebetween whenthe shaft 42 is free to rotate.

In order to retain the steps 68 in resilient engagement with thecooperating steps 58 of the breaker, the shaft 42 is provided with anannular groove 18 wherein there is located a horse-shoe shaped washer 12which bears against the rear wall l6 of the casing to prevent rearwardlateral movement of the shaft relative thereto.

As heretofore indicated, the shaft is normally held against rotation bythe heat responsive element D. More particularly, the element D includesa hollow cylindrical sleeve 14 including an internal bearing 16 forrotatably supporting the shaft. The sleeve 14 is provided forwardly ofthe bearing 16 with a tongue-shaped support 18 which is non-rotatablysecured in the opening of the back wall I6. Rearwardly of the runningbearing 16 the sleeve is internally provided with an undercut annularring 80 and an internally serrated cylindrical surface 82. Formed on theouter end of the shaft and inwardly spaced from 'the serrated surface 82is a serrated cylinder 84 normally secured relative to the sleeve 14 andthe casing C by a fusible material 86 The fusible material 86 may beformed of various low melting point metals, the proportions of which maybe varied so that the mixture will fuse at any desired temperature.

An enclosure 88 seals the rear end of the cylindrical sleeve 14 andprevents the fusible metal in the molten condition from flowing from thecylinder.

The fusible metal 86 normally locks the shaft 42 relative to the frameor casing C and through the engagement of the step 68 with thecooperating steps 58 prevents rotation of the breaker B to the openswitch position Y (Figure 5) However, the metal 86 will fuse if it isheated to the allowable maximum temperature, whereupon the shaft 42 isfree to rotate relative to the casing.

In order to automatically rotate the breaker B to the open switchposition Y, the breaker arm 46 is provided with an anchor pin 98 towhich one end of a spring 92 is secured. The other end of the spring issecured and tensioned to the casing C by an anchor lug 84. Asillustrated in Figures 3 and 4, the anchor lug 84 is upset from the backwall l6 and is located at the corner diagonally opposite from the cornerin which the anchor pin 98 is located when the breaker is in the closedswitch position X. In this position, the spring centrally engages theshaft 42 and is thereby thrown out of alignment with the axis of thebreaker. component of the force exerted by the spring 82 on the breaker'arm 46 in the open switch position X acts through the rotational axisof the breaker and does not tend to rotate the breaker. The minor ortangential component which tends to rotate the arm to open switchposition X is relatively small, and consequently the load on the elementD is not sufficiently great to cause partial failure or defamation ofthe fusible metal lock 86 before the lock reaches the fusingtemperature. Following fusing of the lock 86 the tangential or rotatingcomponent 'of the force produced by the switch becomes increasinglylarger as the breaker rotates from positionX to position Y. Thus theforce produced by the spring is sufficient to cam the resilient switcharms 34 outwardly and insure positive opening of the contacts 36 and 38.

In order to rotate the breaker from the position Y to the position Xfollowing the fusing of the metal lock 86 and its subsequentsolidification, thebreaker is provided with a reset handle H which isconstructed so as to prevent manual rotation of the breaker fromposition X to position Y.

More specifically, the handle comprises a diametrically disposed rib 96,the side walls of which decrease in depth in opposite directions fromend to end. In the embodiment illustrated, the recesses located oneither side of the rib 96 decreases in a counter-clockwise directionwith respect to the cylindrical axis of the breaker from a maximum to anegligible minimum depth. Thusthe side walls of the rib may be graspedby the fingers for rotation in a clockwise direction, but cannot beeffectively grasped so as to enable an operator to manually rotate thebreaker in a counterclockwise direction.

Assuming that the metal 86 has solidified and cooled subsequent to theactuation of the circuit breaker, the breaker may be reset to the closedswitch position X by manual rotation of the handle in a clockwisedirection (Figure 3). The breaker steps 58 will cam the resilient steps68 of However, the major the plate '60 rearwardly until the proceedingsteps 50 at 90 to the previously engaged steps are engaged thereby.

In order to secure the circuit breaker to a chamber, the temperature ofwhich is to be controlled, there is provided outwardly at the back wallIS a pair of rearwardly extending resilient fingers 98 equally spacedfrom the cylindrical sleeve I4, as illustrated in Figure 2. The fingers98 are adapted to secure the circuit breaker to acup-shaped mounting Iand to position the element D within the well I02 formed therein. Moreparticularly, the mounting I00 may be threaded into the wall I04 of aliquid chamber so as to allow the liquid in the chamber to surround thewell I02. With this construction, the temperature of the element D isalways substantially that of the liquid in the chamber.

Figure 4 shows a slightly different type of mounting I00, which may besecured by means of the strap I06 to the cylindrical surface of the wallI04. In this embodiment, the mounting I00 is provided with a cylindricalopening I02, which receives and positions elements D adjacent to thewall I04 of the chamber.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could' be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the followingclaims is intended to cover all of the generic and specific features ofthe invention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

I claim as my invention:

1. An electric circuit breaker including a resilient closed switch, arotatable switch opening member movable from a normal position when theswitch is closed to a second position to positively open the switch, afusible lock for normally holding said switch opening member in normalposition, resilient means for moving said switch opening member to thesecond position when said lock fuses, said resilient means comprising aspring, means carried by the opening member to which one end of thespring is secured, fixed means for securing the other end of the spring,said spring holding means being diametrically opposite when the openingmember is in normal position, and means aligned with the axis of theopening member for deflecting the spring out of a straight line when theswitch opening member is in normal position whereby said spring willhave a minimum rotational effect on said member in the normal positionand a maximum effect in the second position.

2. An electric circuit breaker comprising a normally closed switch, arotatable supporting shaft, a fusible lockdirectly engageable with thesupporting shaft for normally holding said shaft against rotation, aswitch opening member mounted on the shaft for rotation between a normalposition where said switch is closed to a second position where it openssaid switch, spring means normally tending to'rotate said shaft fromnormal to second position, and means on the shaft engageable with meanson said switch opening member upon rotation of the opening member fromnormal position to second position and disengageable upon rotation fromsecond to normal position.

3. An electric circuit breaker including a normally closed switch, arotatably supported shaft, a cylindrical switch opening memberjournalled on the shaft for rotation between a normalposition when saidswitch is closed to a second position when it opens said switch, afusible lock for normally holding the shaft against rotation, auni-directional drive between the switch opening member and shaftengageable upon rotation of the opening member from normal position tosecond position and disengageable upon rotation from second position tonormal position, a spring for rotating said opening member, said springhaving one end secured to the opening member and its other end fixed ata point diametrically opposite the other end when said opening member isin normal position, said spring extending when said opening member is innormal position across said shaft and biased out of diametric alignmentby said shaft to thereby have a minimum rotational effect on saidopening member in its normal position and a maximum effect in the secondposition.

4. An electric circuit breaker comprising a casing, a normally closedswitch mounted in the casing, a shaft rotatably supported in the casing,

a switch opening member journalled on the shaft between a normalposition and a second position, said member having a handle portionextending out of the casing and manually engageable for rotation in onedirection only, a lug on said opening member for camming the switch toopen position when the member is in said second position, a fusible lockfor normally holding the shaft against rotation, a uni-directional drivebetween the member and shaft engageabie upon movement of the member fromnormal to second position and disengageable upon movement from second tonormal position, a spring having one end secured to the switch openingmember and its other end to the casing at a point diametrically'opposite to its fixed end when the switch opening member is in normalposition, said spring being slightly biased out of diametric alignmentby said shaft to produce a minimum rotational effect on said switchopening member in normal position and a maximum effect in the secondposition.

5. An electric circuit breaker comprising a casing, a normally closedswitch within the casing including a rotatable supporting shaft, 9.fusible lock normally holding said shaft against rotation, aswitchopening member mounted on said shaft, interengaging means on saidshaft and member allowing free rotation of the opening member in onedirection and engagin said member with the shaft when rotated in theother direction, spring means normally tending to rotate said member tocause said interengaging means to engage, means carried by said openingmember for securing one end of said spring, fixed means in said casingfor securing the other end of the spring, the means for securing theends of the spring being disposed to opposite sides of said shaft and indiametric' alignment with one another and said shaft when said switch isin normally closed position, whereby the intermediate portion of thespring will be biased out of alignment by said shaft.

HAROLD W. BIRK.

